There are currently an estimated 40,000 incidences of cardiac arrest every year in Canada, most of which take place outside of hospital settings. The odds of an out-of-hospital cardiac arrest currently stand at approximately 5%. In the U.S., there are about 164,600 such instances each year, or about 0.55 per 1000 population. It may be desirable to decrease the number of deaths resulting from these out-of-hospital incidences of cardiac arrest. Certain places, such as sports arenas, and certain individuals, such as the elderly, are at particular risk and in these places and for these people, a convenient solution may be the difference between survival and death.
Cardiopulmonary resuscitation (CPR) is a proven effective technique for medical and non-medical professionals to improve the chance of survival for patients experiencing cardiac failure. CPR forces blood through the circulatory system until professional medical help arrives, thereby maintaining oxygen distribution throughout the patient's body. However, the quality of CPR is often poor. Retention of proper CPR technique and protocol may be inadequate in most individuals and the anxiety of an emergency situation may confuse and hinder an individual in delivering proper treatment.
According to the Journal of the American Medical Association (2005), cardiopulmonary resuscitation (CPR) is often performed inconsistently and inefficiently, resulting in preventable deaths. Months after the completion of standard CPR training and testing, an individual's competency at performing effective chest compressions often deteriorates significantly. This finding was found to hold true for untrained performers as well as trained professionals such as paramedics, nurses, and even physicians.
The International Liaison Committee on Resuscitation in 2005 described an effective method of administering CPR and the parameters associated with an effective technique. Parameters include chest compression rate and chest compression depth. Chest compression rate is defined as the number of compressions delivered per minute. Chest compression depth is defined as how far the patient's sternum is displaced by each compression. An effective compression rate may be 100 chest compressions per minute at a compression depth of about 4-5 cm. According to a 2005 study of actual CPR administration at Ulleval University Hospital in Norway, on average, compression rates were less than 90 compressions per minute and compression depth was too shallow for 37% of compressions.
According to the same study, CPR was often administered when unnecessary or was not administered when necessary. The study found that compressions were not delivered 48% of the time when cardiovascular circulation was absent.
Other studies have found similar deficiencies in the delivery of CPR. One 2005 study at the University of Chicago found that 36.9% of the time, less than 80 compressions per minute where given, and 21.7% of the time, less than 70 compressions per minute were given. The chest compression rate was found to directly correlate to the spontaneous return of circulation after cardiac arrest.
In addition to too shallow compressions, too forceful compressions may also be problematic. Some injuries related to CPR are injury to the patient in the form of cracked ribs or cartilage separation. Such consequences may be due to excessive force or compression depth. Once again, lack of practice may be responsible for these injuries.
Positioning of the hands is another parameter that may be considered when delivering CPR. It has been found that an effective position for the hands during compression is approximately two inches above the base of the sternum. Hand positioning for effective CPR may be different depending on the patient. For example, for performing CPR on an infant, an effective position may be to use two fingers over the sternum.
Therefore, a device to facilitate the proper delivery of CPR in an emergency may be useful. Furthermore, a device that can also be used in objectively training and testing an individual may be useful for the CPR training process and protocol retention.
There are currently mechanical systems for the delivery of CPR that may be used in a hospital setting. Chest compressions may be delivered through a mechanism comprising mechanical movement (e.g., piston movement or motor movement). One such device is the AutoPulse™ by Revivant Corp, which has a computer-controlled motor attached to a wide chest band that compresses the patient's chest, forcing blood to the brain when the heart has stopped beating. Such a device is cumbersome and heavy to transport, requires time to set up and activate, and is expensive. Such devices have shown inconclusive results in studies trying to determine their effectiveness at increasing survival rates from cardiac arrest.
U.S. Pat. No. 6,351,671 discloses a device that measures the chest impedance of a patient as well as the force of active chest compressions. From these calculations, the device indicates to the user when a successful compression has been completed. However, this technology requires defibrillator pads to be placed across the chest of the patient and is, consequently, relatively time consuming to activate. The commercially available device, Q-CPR® by Phillips Medical, must be attached to an expensive hospital-grade defibrillator making it expensive, heavy and inaccessible to the lay user. Furthermore, this technology relies heavily on data collected from an accelerometer. Many current technologies are based around accelerometer technology.
Another device using accelerometer technology for the determination of compression depth is disclosed in U.S. Pat. No. 7,074,199. Any acceleration data from accelerometers used to measure the depth of chest compression during CPR is prone to cumulative errors and drift errors. Consequently, these sensors are not suitable for highly accurate or detailed data collection regarding CPR parameters and can only be relied on for approximate depth values. Furthermore, the use of an accelerometer in a CPR monitoring device without an external reference is prone to error if the patient or rescuer is mobile. For example, if the patient is being medically transported in an ambulance, helicopter or on a gurney, the accelerometer is unable to differentiate between the external movement of the patient and the compressions of the chest. In any type of non-stationary environment, an accelerometer based device may be unreliable and ineffective. The use of an accelerometer to calculate compression depth also relies on complicated and error-prone calculations to compensate for the angle and tilt of the compression device. If the accelerometer is not perfectly level on the chest of the patient and its movement is not perfectly vertical, errors may accumulate and must be accounted for by the angle of the two horizontal axes. Furthermore, the absence of any external reference point makes it difficult for the device to know its position in space at any given time. All measurements of distance are relative and an origin of movement is difficult to ascertain and maintain over the course of measurements. This may cause the initiation or starting point of the compressions to drift over time leading to errors in depth measurements. Certain commercial products currently use accelerometer technology, such as the AED Plus® D-Padz® from Zoll Medical, in which the accelerometer is embedded into the pads of the defibrillator. Due to the additional circuitry and sensory within them, these defibrillator pads are substantially more expensive and must be disposed of after each use. Therefore, relatively expensive sensory must be routinely discarded due to the design of the product.
U.S. Patent Application Publication No. 2007/0276300 to Kenneth F. Olson et al. discloses a device using ultrasound transmission to calculate compression depth. An acoustic signal is transmitted from a device on the chest of the patient to a receiver in another location. This device has several drawbacks. First, the ultrasound signal must have a clear line of sight from transmitter to receiver in order to operate. Any interference, objects, people or even the hand of the rescuer in the way of the signal may result in signal loss or deterioration. The transmitter must be directed toward the receiver and the relative orientation between the transmitter and receiver is crucial. Second, ultrasound is relatively slow and a time-of-flight measurement of an ultrasound signal may suffer from significant lag and latency. Third, an ultrasound signal is highly dependent on ambient conditions such as air temperature. If air temperature fluctuates, so does the speed of sound, which may result in inaccuracies. Finally, if the plane of the chest compression is initially unknown, the calculation of compression depth may be significantly compromised. Time-of-flight ultrasonic distance interpolation cannot resolve the position of the receiver in six degrees of freedom and the determination of the downward translational movement if the patient, receiver or transmitter is not level may be difficult. Even if ultrasonic triangulation is employed, latency may be significant, resolution may be low and multiple transmitters and receivers in different locations may be required.
It may be desirable to provide an easy-to-use and inexpensive device to accurately measure relevant CPR parameters such as compression depth and rate absent of the problems in the aforementioned technologies. Additionally, it may be useful for the device to provide instructions for carrying out CPR procedure for training, testing, and/or emergency situations.